Calculating Induced EMF in a Circular Loop Antenna

Click For Summary
SUMMARY

The discussion focuses on calculating the maximum induced electromotive force (emf) in a circular loop antenna with a diameter of 22.0 cm, positioned 2.20 km from a 95.0 MHz source emitting 55.0 kW of power. The user initially attempted to derive the power received by the loop using the ratio of the loop's area to the surface area of a sphere at the given distance, resulting in 3.43 x 10^-5 W. The conversation highlights the application of Faraday's law of induction, specifically EMF = d(phi)/dt, where phi is the magnetic flux through the loop. The user calculates the maximum magnetic field (Bmax) and magnetic flux but struggles to find the correct method to derive the induced emf.

PREREQUISITES
  • Understanding of electromagnetic theory, specifically Faraday's law of induction.
  • Familiarity with the concepts of magnetic flux and induced emf.
  • Knowledge of power calculations in electromagnetic fields.
  • Basic proficiency in unit conversions and working with SI units.
NEXT STEPS
  • Study the derivation and application of Faraday's law of induction in various contexts.
  • Learn how to calculate magnetic flux and its relation to induced emf in antennas.
  • Research the relationship between power, intensity, and electric/magnetic fields in electromagnetic waves.
  • Explore practical examples of antenna theory and design, focusing on circular loop antennas.
USEFUL FOR

Physics students, electrical engineers, and anyone involved in antenna design or electromagnetic theory who seeks to understand the principles of induced emf in circular loop antennas.

AStaunton
Messages
100
Reaction score
1
the problem given is:
A circular loop of wire can be used as a radio antenna. If a 22.0-cm-diameter antenna is located 2.20km away from a 95.0-MHz source with a total power of 55.0kW, what is the maximum emf induced in the loop? (Assume that the plane of the antenna loop is perpendicular to the direction of the radiation's magnetic field and that the source radiates uniformly in all directions.)

As far as I have gotten in solving the problem:
as the loop of wire is at a distance of 2.2km from transmitter we want to find how much energy the loop of wire is getting:

((area of loop of wire)/(surface area of 2.2km sphere))*(power of transmitter)

and plugging numbers in (in mks units) gives:

((.11^2*pi)/(2200^2*pi)*55000) = 3.43*10^-5W

I would be very grateful for a nudge in the right direction...I'm fairly sure there must be a convenient equation derived from laws of inductance that links the power going through the loop, the Frequency (95Mhz) and the induced Voltage which is the variable I want to find.

Thanks

Andrew
 
Physics news on Phys.org
it occurs that maybe the relevant equation here is simply:

P = VI

where as I already stated P for the loop = 3.43*10^-5W

still can't figure what should be done from here...

Still not positive that P = VI is that right eqtion to use!
 
futher update:

forget that P = VI crap!

it seems that this problem involves Faraday's law:

EMF= d(phi)/dt

so as loop as perpendicular to propagation, phi is simply B*A.

A=.11^2*3.14 ---> as per the values given in the problem..

to find B:

we know intensity, I:

55000/(22000^2*4*3.14) = 9.05*10^-4 W/m^2

also we know I = EmaxBmax/2(mu_0)

so can find Bmax from this:
=> Bmax = 2.76(10^-9)

so (phi) = Bmax*A=1.048(10^-10)

so to find d(phi)/dt is it simply a matter of dividing the above value by the frequency that was told in the question (95MHz)?

But this apparently is not the correct answer...

Be very grateful if someone could inform me of whatever mistakes I am making...cheers
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
5K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
4
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 5 ·
Replies
5
Views
4K